Position oven racks in the upper and lower thirds of the oven; heat to 375 degrees. Line a
rimmed baking sheet with parchment paper.

Toss the florets, oil and salt in a mixing bowl to coat. Spread the florets on the baking sheet,
flat edges down. (Wipe out the bowl; you’ll use it again.)

Bake on the lower rack for 20 minutes, then turn the oven on broil. When it’s heated, transfer
the cauliflower to the top rack and broil for 7 to 10 minutes, until nicely browned and tender.
Keep the broiler on.

Transfer the florets to the same bowl you first used. Add the cream, garlic, Gruyere cheese,
half of the Parmigiano-Reggiano and all the pepper and nutmeg. Stir to incorporate, then spoon the
cauliflower into a large gratin dish.

Sprinkle with the remaining Parmigiano-Reggiano and return to the broiler for 5 minutes, until
golden brown and bubbly.